cutting thread tips off for 70% thread - is there formula?
cutting thread tips off for 70% thread - is there formula?
(OP)
When cutting threads on a lathe... is there a formula somewhere in the machinist handbook if you want to have only 70% engagment to help prevent galling or do you just take major dia minus minor dia (for internal and external) and multiply by .7 and use that number to figure it out? just taking the tips off to help prevent galling
thanks
thanks





RE: cutting thread tips off for 70% thread - is there formula?
While I'm not sure if it covers your specific case it has a bunch of info on modified/special/different UN forms that may be of use to you. It may be that there's a standard modified thread form you could use.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: cutting thread tips off for 70% thread - is there formula?
If you are talking about reducing the pitch diameter of the thread then I think you need to talk about the class of fit rather than percent engagement.
RE: cutting thread tips off for 70% thread - is there formula?
and yes its for those 1 1/4-8 UN threads... I will look at b1.1 I have copy somewhere around the office
RE: cutting thread tips off for 70% thread - is there formula?
RE: cutting thread tips off for 70% thread - is there formula?
RE: cutting thread tips off for 70% thread - is there formula?
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RE: cutting thread tips off for 70% thread - is there formula?
RE: cutting thread tips off for 70% thread - is there formula?
I would agree with Compositepro. Reducing the OD of the external thread body will not reduce galling, since most thread spec dimensions are established to prevent interference between the external tips and internal roots.
In the absence of preload, the most common cause of thread galling is interference at the engaged thread flanks. This can be caused by pitch error accumulation, pitch diameter runout, or other such profile errors. You can solve the galling issue by reducing the engaged thread length, reducing pitch/profile errors, or by increasing the clearance between the mating threads.
Using a reduced tolerance class (ie. cl.2 vs cl.3) will result in a "looser" thread, but you will also need to make allowances for this less accurate fit in your loads analysis.
Good luck.
Terry
RE: cutting thread tips off for 70% thread - is there formula?